1. Field of the Invention
This invention relates to vacuum packages and vacuum packaging equipment, and particularly to a resealable package configuration and apparatus for producing same. Such packages are particularly useful for food products where the package is evacuated and hermetically sealed, and where the consumer wishes to reclose the package after breaking the hermetic seal.
Many food items, such as bacon, hot dogs, cheese, luncheon meat, etc., are sold in vacuum packages formed from flexible thermoplastic materials. The packages are evacuated and hermetically sealed, and in some cases gas flushed, to preserve the freshness of the product within the package. However, the consumer often does not use all of the product immediately, and may therefore want to reclose the package. It is undesirable for the consumer to have to entirely repackage the product in, for example, a cellophane or Saran (trademark) wrap or sealable bag. Many prior art package designs therefore offer means for resealing the package.
One such means involves the use of zipper-type resealable closure strips on the two inner surfaces of the package material. These closure strips consist of thermoplastic beads either extruded with or attached to the package materials. These beads have an interlocking profile. A number of patents have been issued for such packages in the past, including those briefly described below.
2. Description of the Prior Art
Patents issued in the past relating generally to resealable packages include, for example, the following U.S. Pat. Nos: 2,991,001, 3,473,589, 3,780,781, 3,815,317, 4,240,241, 4,246,288, 4,572,377, 4,437,293, 4,617,683, 4,698,954, and U.S. Pat. No. 4,782,951.
Included in the above list are three United States patents assigned to W. R. Grace & Co., naming Sanborn, Jr. as inventor. Pat. No. 4,240,241, issued Dec. 23, 1980, and Pat. No. 4,437,293, issued Mar. 20, 1984, claim a method and apparatus for making a reclosable package. U.S. Pat. No. 4,246,288, issued Jan. 20, 1981, claims the reclosable package itself. The reclosable package comprises an external peripheral seal and a reclosable seal on the interior side of one edge of the package. "Indentations" are punched out to remove a portion of zipper bead material in the region of the sealed area, though a central strip of material still remains.
Also included in the above list is U.S. Pat. No. 4,782,951 (Griesbach et al), granted on Nov. 8, 1988 and assigned to Oscar Meyer Foods Corporation. This patent discloses a reclosable package having interlocking closure strips positioned outside of a hermetic seal. The hermetic seal is of the peelaway type so as not to destroy the integrity of the package upon opening of the package.
The main problem in the prior art, as well described in the Oscar Meyer and Sanborn patents in particular, is that of sealing through a resealable closure or "zipper". Sealing around the zipper beads is difficult, and all too frequently small leaks result, especially after the package has been handled in transit. In the Oscar Meyer patent, the solution to this problem is to locate the zipper outside the sealed area. Though advantageous in some respects, this poses problems of its own, principally the problem that the relatively expensive "peelable" seal is essential. In the Sanborn patents, the solution is to punch out "indentations" to remove some of the zipper bead material, though as mentioned above a central strip of the zipper substrate remains.